Processes using dividing wall distillation column

ABSTRACT

A method for the separation of hydrocarbon compounds utilizing a dividing wall distillation column is described. The dividing wall distillation column enables one or more side draw stream to be removed from the dividing wall distillation column in addition to an overhead stream and a bottoms stream.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of prior U.S. patent application Ser.No. 12/347,922, filed Dec. 31, 2008, now U.S. Pat. No. 7,956,157, issuedJun. 7, 2011.

TECHNICAL FIELD

This disclosure relates to the use of distillation to achieve impurityremoval or separation of compounds from process streams. Morespecifically, this disclosure relates to the use of distillation toachieve separation of compounds such as ethylbenzene (EB) andpolyethylbenzenes (PEB) from an alkylation process; separation ofcompounds such as ethylbenzene (EB), xylenes and styrene from a styreneor polystyrene production process; and separation of benzene, tolueneand xylene from a mixed BTX stream.

BACKGROUND

Styrene, also known, as vinyl benzene, is an aromatic compound that canbe produced in industrial quantities. The most common method of styreneproduction comprises the dehydrogenation of EB, which produces a productstream that includes styrene, EB and PEBs. It is desirable to reduce theamount of EB and PEBs in the polystyrene product.

Polystyrene is an aromatic polymer produced from the styrene monomer.Polystyrene is a widely used polymer found in insulation, packaging,disposable cutlery, and in foamed application such as for drinking cups.During the production of polystyrene, impurities including EB can enterwith the fresh styrene feed or from a recycle stream. The EB can exitthe process as a purge stream, or in the composition of the polystyreneproduct. It can be desirable to reduce the amount of EB in thepolystyrene product.

Separation of EB from the crude styrene product or in the purge streamof a polystyrene process can be difficult due to the similar boilingpoints of EB and styrene. The use multiple distillation columns is thetypical means of component separation.

The alkylation of benzene to produce ethylbenzene is a common commercialreaction included in the production of styrene. The separation of theproducts of such a reaction is typically accomplished by a series ofdistillation steps. Likewise the separation of product streams such asBTX, a mixture of benzene, toluene and xylene, is also typicallyaccomplished by a series of distillation steps.

The use of process schemes incorporating multiple distillation columnscan be costly and inefficient. Thus, it would be desirable accomplishcomponent separation utilizing a reduced number of distillation columnsby a method that is more economically viable.

SUMMARY

Disclosed herein is a method for the separation of hydrocarbon compoundsthat includes obtaining a first stream comprising hydrocarbon compoundsand sending at least a portion of the fast stream to a dividing walldistillation column comprising a dividing wall. An overhead stream and abottoms stream are removed from the dividing wall distillation columnalong with a side draw stream. The first stream enters the dividing walldistillation column on an opposing side as the side draw stream and thefirst stream inlet and the side draw stream outlet are separated by thedividing wall. The first stream can be fed to the dividing walldistillation column at a location above where the side draw stream istaken. A second side draw stream can be removed from the dividing walldistillation column at a point lower than the side draw stream and isalso on an opposing side as the first stream.

The first stream can be produced from a first reaction zone. At least aportion of the overhead stream, side draw stream or bottoms stream canbe recycled as feed to the first reaction zone. The first stream can bea reactor effluent stream from a polystyrene reaction zone where theside draw stream comprises styrene that can be recycled to thepolystyrene reaction zone. At least a portion of the first stream can berecycled to the polystyrene reaction zone. The overhead stream cancomprise ethylbenzene.

The first reaction zone can produce a first stream comprising styreneand can be an ethylbenzene dehydrogenation reaction zone.

The first reaction zone can be a benzene alkylation reaction zone thatproduces a first stream comprising ethylbenzene where the overheadstream comprises benzene, the side draw stream comprises ethylbenzeneand the bottoms stream comprises polyethylbenzene. The bottoms streamcan be fed to a transalkylation reaction zone and produce a secondstream that has a lower polyethylbenzene content than the bottomsstream. A portion of the second product stream can be fed to thedividing wall distillation column.

A second side draw stream can be removed from the dividing walldistillation column at a point lower than the side draw stream. Thesecond side draw stream can comprise polyethylbenzene and be fed to atransalkylation reaction zone to produce a second stream that has lowerpolyethylbenzene content than the second side draw stream. All or aportion of the second product stream can be fed to the dividing walldistillation column.

In one embodiment the first stream comprises at least two of benzene,toluene, xylene or ethylbenzene and the dividing wall distillationcolumn can produce an overhead stream comprising benzene, a side drawstream comprising toluene and a bottoms stream comprising xylene. Asecond side draw stream from the dividing wall distillation column canbe removed at a point lower than the side draw stream, wherein thesecond side draw stream comprises polyethylbenzene.

Another embodiment of the invention is a method of polystyreneproduction by feeding a stream comprising styrene to a polystyrenereaction zone, wherein a stream comprising polystyrene is removed and areactor effluent stream is removed. At least a portion of the reactoreffluent stream is sent to a dividing wall distillation column where anoverhead stream, a bottoms stream and a side draw stream are removedfrom the dividing wall distillation column, the side draw streamcomprising styrene. The feed stream can comprise styrene mixed with asolvent prior to entering the polystyrene reaction zone, the solventcomprising paraffin boiling in the range of from 135° C. to 150° C. Thereactor effluent is fed to the dividing wall distillation column at alocation above where the side draw stream is taken. The side draw streamcan be recycled to the polystyrene reaction zone. A portion of thereactor effluent stream can be recycled to the polystyrene reactionzone. The reactor effluent stream can include styrene and ethylbenzene.The overhead stream can include ethylbenzene.

Yet another embodiment is a method of styrene production that includesobtaining a first product stream from a styrene reaction zone andsending at least a portion of the first product stream to a dividingwall distillation column. An overhead stream, bottoms stream and a sidedraw stream are removed from the dividing wall distillation column. Thefirst product stream can be fed to the dividing wall distillation columnat a location above where the side draw stream is taken. The side drawstream can include styrene and the overhead stream can includeethylbenzene. At least a portion of the overhead stream can be recycledto the styrene reaction zone.

Still another embodiment is a method of ethylbenzene production thatincludes obtaining a first product stream from an alkylation reactionzone and sending at least a portion of the first product stream to adividing wall distillation column. An overhead stream, bottoms streamand a side draw stream are removed from the dividing wall distillationcolumn. The first product stream can be fed to the dividing walldistillation column at a location above where the side draw stream istaken. The side draw stream can include ethylbenzene and the overheadstream can include benzene. At least a portion of the overhead streamcan be recycled to the alkylation reaction zone. The bottoms stream caninclude polyethylbenzene and at least a portion of the bottoms streamcan be fed to a transalkylation reaction zone to produce a secondproduct stream that has reduced polyethylbenzene content than thebottoms stream. At least a portion of the second product stream can befed to the dividing wall distillation column.

Disclosed herein is a method for production of polystyrene, wherein adividing wall distillation column is used for impurity removal andstyrene recovery from the reactor effluent. More specifically, disclosedherein is a method for production of polystyrene wherein a polystyrenereactor effluent is sent to a dividing wall distillation column, whereinthe dividing wall distillation column produces a light cut stream, aheavy cut stream, and a recycle stream containing styrene.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a prior art distillation separation process with multipledistillation columns not having a side draw.

FIG. 2 shows a polystyrene process having a purge stream separated usingmultiple distillation columns not having a side draw.

FIG. 3 shows a polystyrene process having a purge stream separated usinga dividing wall distillation column having a side draw.

FIG. 4 shows a production process incorporating a dividing walldistillation column having two side draws, one side draw being a recyclestream.

FIG. 5 shows a production process incorporating a dividing walldistillation column having two side draws, one side draw being a recyclestream having a second separate reaction zone.

FIG. 6 is a schematic illustration of a dividing wall distillationcolumn having two side draws along with an overhead and bottoms outletstreams.

DETAILED DESCRIPTION

Disclosed herein are methods for the separation of hydrocarbon compoundsthat includes a dividing wall distillation column comprising a dividingwall. The dividing wall vertically bisects a portion of the interior ofthe distillation column but does not extend to the top or bottomsections of the column, thus enabling the column to be refluxed andreboiled similar to a conventional column. The dividing wall provides afluid impermeable baffle separating the interior of the column. Theinlet to the column is located on one side of the dividing wall whileone or more side draws are located on the opposing side. The dividingwall enables the side of the column that does not have the inlet tofunction in a more stable manner with minimal effect from fluctuationsin inlet flow rates, conditions or composition. This increased stabilityenables the column to be designed and operated in a manner that allowsone or more side draw streams to be removed from the column havingdifferent compositions from either the overhead stream or the bottomsstream.

The ability to make three or more product streams from a single columncan enable component separation with fewer distillation columns andpossibly reduced capital costs. The dividing wall distillation columncan be used as a sole distillation column or multiple dividing walldistillation column can be used, either in series or parallelarrangements. The dividing wall distillation column can also be used inconjunction with one or more conventional distillation column.Embodiments of the present invention can be particularly applicable whenthe optimum feed location to the column is above the optimum side drawlocation. If the feed location is above the side draw location in aconventional distillation column, the downward flow of the liquid feedwithin the column will have a significant effect on the side drawcomposition. Variations in the feed flow rate, conditions or compositionof the feed stream will alter the side draw composition and make theproduction of a stable side draw stream very difficult to achieve.

Disclosed herein is a method for production of polystyrene wherein apolystyrene reactor produces one stream comprising polystyrene and asecond stream of reactor effluent, wherein the reactor effluent is sentto a dividing wall distillation column, wherein the dividing walldistillation column can produce a light cut, heavy cut, and styrenerecycle streams.

The styrene feed to a polystyrene reactor may include contaminantsincluding ethyl-benzene. Ethyl-benzene, as well as other aromatics, istypically allowed to build up in the process in order to create adilutant for the reaction. A dilutant can be utilized to absorb the heatof reaction, and thereby control the polymerization reaction rate andprevent a runaway reaction. Other aromatic impurities may includeortho-xylene, meta-xylene, cumene, n-propylbenzene and MPET and as agroup herein referred to as other aromatic impurities.

It can be advantageous to reduce the content of ethyl-benzene in thepolystyrene product. The amount of ethyl-benzene contained in thepolystyrene pellets is proportional to the amount of ethyl-benzene inthe reactor, approximately one pound of ethyl-benzene leaves in thepellets for every thousand pounds of ethyl-benzene that leaves thereactor.

The styrene feed can also include a solvent, for example, Isane 130. Inan illustrative example, the styrene feed may comprise between 75 and99.5 weight percent styrene, from 0 to 20 weight percent Isane 130, and10 ppm to 5000 ppm ethyl-benzene. As a further example, the styrene feedmay comprise between from 85 to 95 weight percent styrene, from 7 to 12weight percent Isane 130, and 100 ppm to 1000 ppm ethyl-benzene.

The solvent, Isane 130, is a commercial name for a solvent sold by TOTALPetrochemicals USA, Inc. The solvent is composed of paraffins having aboiling point range of between about 135 to about 150 degrees Celsius.The composition of Isane 130, as determined by ASTM D86, is representedin Table 1 below.

TABLE 1 Component Mass Fraction 2,4-DIMETHYLHEXANE 0.0220542,3,3-TRIMETHYLPENTANE 1.10E−15 3-METHYLHEPTANE 0 N-OCTANE 02,4,4-TRIMETHYLHEXANE 0.13726 2,2,3,4,-TETRAMETHYLPENTANE 0.199912,6-DIMETHYLHEPTANE 0.31968 2,2,3,3-TETRAMETHYLPENTANE 0.239613-METHYLOCTANE 0.051423 N-NONANE 0 3,3,5-TRIMETHYLHEPTANE 02,6-DIMETHYLOCTANE 0.0002 4-METHYLNONANE 0.000353 DECANE 0.029509

Isane 130 can be a good solvent for a polystyrene process, because abulk of the solvent boils between styrene and ethyl-benzene andtherefore increases the relative volatility between styrene andethyl-benzene. Thus, the addition of Isane 130 solvent in the styrenefeed composition can make the task of separating styrene andethyl-benzene easier.

A polystyrene reaction zone produces polystyrene and an effluent stream.A portion of the effluent stream can be taken as a purge stream tomaintain the composition of aromatics other than styrene in the process.The effluent stream can be recycled to the inlet of the polystyrenereaction zone and/or added with fresh styrene feed to the reactor.

In accordance with an embodiment of the invention, at least a portion ofthe reactor effluent can be sent to a distillation column for impurityremoval. According to one embodiment of the invention, 0.01 to 99.99weight percent is recycled to the polystyrene reaction zone, while theremaining portion is sent to a distillation column. According to anotherembodiment of the invention, 50 to 95 weight percent of the effluent isrecycled, while the remaining portion is sent to a distillation column.According to yet another embodiment, 75 to 95 weight percent is recycledto the polystyrene reaction zone, while the remaining portion is sent toa distillation column.

In accordance with another embodiment of the invention, all of thereactor effluent is sent to a distillation column.

In accordance with the invention, the distillation column comprises aninterior dividing wall and can be referred to as a dividing walldistillation column. In this embodiment, the feed tray and the side drawtray are on opposite sides of the dividing wall. In this dividing wallcolumn arrangement, the dividing wall acts as a barrier to prevent theentering feed from affecting the composition of the side draw stream.This arrangement allows for the feed tray to be in a position above theside draw tray. Therefore, the dividing wall column arrangement allowsfor a sidedraw to be taken from the same column that a feed streamenters.

According to an embodiment of the invention, the dividing wall recoverycolumn comprises between 20 and 100 equilibrium stages, or trays.According to another embodiment, the dividing wall recovery columncomprises between 30 and 90 trays. According to yet another embodiment,the dividing wall recovery column comprises between 40 and 80 trays. Thecolumn may contain any suitable type packing or trays such asnon-limiting examples sieve or bubble trays.

According to the embodiments, the feed tray is located on the oppositeside of the dividing wall as the side draw tray. According to anembodiment, the feed tray is located at or above the side draw tray.According to another embodiment, the feed tray is located below the sidedraw tray.

The invention disclosed herein can be utilized for separatingethyl-benzene from styrene. According to embodiments of this styreneseparation process, a styrene and ethyl-benzene mixture is fed to adividing wall distillation column. The dividing wall distillation columnseparates the styrene and ethyl-benzene mixture into up to four separatestreams. These four separate streams comprise an overhead productcomprising ethyl-benzene, a side draw product comprising styreneproduct, a lower side draw stream comprising polyethylbenzene, and abottoms residue stream,

In accordance with the embodiments, the styrene and ethyl-benzenemixture fed to the dividing wall distillation column is obtained fromthe product stream of a styrene production process. In an embodiment, astyrene reactor product is sent directly to the dividing walldistillation column for styrene recovery.

The invention disclosed herein can be utilized for separating aromaticcompounds such as mixtures of benzene, toluene, xylenes andethylbenzene. According to embodiments of this aromatic separationprocess, an aromatic mixture is fed to a dividing wall distillationcolumn. The dividing wall distillation column separates the componentsinto up to four separate streams. These four separate streams cancomprise an overhead product comprising benzene, a side draw productcomprising toluene, and a bottoms stream of xylenes and ethylbenzene. Analternate aromatic separation can be the separation of a BTX(benzene-toluene-xylene) stream into an overhead product comprisingbenzene, a side draw product comprising toluene, and a bottoms stream ofxylene.

The invention disclosed herein can be utilized for separating productsfrom an alkylation reaction, such as the alkylation of benzene toethylbenzene. The products can include benzene, ethylbenzene andpolyethylbenzenes. The dividing wall distillation column separates thecomponents into up to four separate streams. These four separate streamscan comprise an overhead product comprising benzene, an upper side drawproduct comprising ethylbenzene, a lower side draw product comprisingpolyethylbenzenes and a bottoms stream of heavier components such astetraethylbenzene.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a separation process utilizing two distillation columnsfor the separation of components according to prior art. The firstdistillation column (130) separates an inlet stream (111) into anoverhead stream (131) and a bottoms stream (134) that will comprisestyrene. The overhead (131) is condensed in condenser (132), resultingin stream (133). A portion of the condensed stream (133) can be refluxedto the first distillation column (130). A portion of bottoms stream(134) is sent back into the column via reboiler (135), while theremaining bottoms is withdraw in line (136).

The bottoms stream (136) is sent to a second distillation column (140)that produces an overhead stream (141) and a bottoms stream (144). Theoverhead (141) is condensed in condenser (142), resulting in stream(143), a portion of which can be refluxed to the second distillationcolumn (140). A portion of bottoms stream (144) is sent back into thecolumn via reboiler (145), while the remaining bottoms is withdraw inline (146).

FIG. 2 depicts a polystyrene process utilizing two distillation columnsfor the treatment of the reaction effluent stream according to priorart. Styrene feed (102) is mixed with a styrene recycle stream (118),resulting in a mixed polystyrene reactor feed (104).

The polystyrene reactor (107) produces a polystyrene product (106) andan effluent stream (109).

A portion of the effluent (109) can be purged in stream (110) orrecycled back to the mixed polystyrene reactor feed (104). The remainingeffluent (111) that is not purged or recycled is sent to a firstdistillation column (130). The first distillation column (130) separateseffluent (111) into an overhead stream (131) and a bottoms stream (134)that will comprise styrene. The overhead (131) is condensed in condenser(132), resulting in stream (133). A portion of bottoms stream (134) issent back into the column via reboiler (135), while the remainingbottoms is withdraw in line (136).

The bottoms stream (136) is sent to a second distillation column (140)that produces an overhead stream (141) that comprises styrene and abottoms stream (144). The overhead (141) is condensed in condenser(142), resulting in recycle stream (143). A portion of bottoms stream(144) is sent back into the column via reboiler (145), while theremaining bottoms is withdraw in line (146).

The recycle stream (143), comprising styrene, can be sent to a heatexchanger (117) to obtain a liquid styrene stream (118), which is thenmixed with the styrene feed (102).

FIG. 3 depicts an embodiment of the invention, wherein a single dividingwall recovery column is applied to the polystyrene process. Styrene feed(102) is mixed with Isane solvent (103), an effluent recycle stream(110) and a styrene recycle stream (118), resulting in a mixedpolystyrene reactor feed (104).

The polystyrene reactor (107) produces a polystyrene product (106) andan effluent stream (109).

A portion of the reactor effluent stream (109) is then optionally sentto a purge or a recycle in stream (110). The remaining effluent (111)that is not purged or recycled is sent to the dividing wall distillationcolumn (112). The dividing wall distillation column (112) separateseffluent (111) into an overhead stream (113), a styrene recycle stream(116), and a bottoms stream (119). The overhead (113) is condensed incondenser (114), resulting in stream (115). The recycle stream (116),comprising styrene, can be sent to a heat exchanger (117) to obtain aliquid styrene stream (118), that is then mixed with the styrene feed(102) and Wile solvent (103). A portion of bottoms stream (119) is sentback into the column via reboiler (120), while the remaining bottoms iswithdraw in line (121).

FIG. 4 illustrates an embodiment of the invention, wherein the dividingwall column distillation is used to produce two side draw streams. Afeed (202) is mixed with a recycle stream (218), resulting in a mixedreactor feed (204) that is fed to reactor (208). The reactor (208)produces product stream (209).

The product stream (209) is then sent to a dividing wall distillationcolumn (212) that separates product stream (209) into an overhead stream(213), an upper side draw stream (222), a lower side draw recycle stream(216), and a bottoms residue stream (219). The overhead (213) iscondensed in condenser (214), resulting in stream (215). The recyclestream (216) can be sent to a heat exchanger (217) to obtain recyclestream (218), that is then mixed with the feed (202). A portion ofbottoms residue stream (219) is sent back into the column via reboiler(220), while the remaining bottoms residue is withdraw in line (221).Optionally any of the streams (215, 222, 216 or 221) can be used as therecycle stream depending on the particular components being separatedand the particular products being produced.

FIG. 5 illustrates an embodiment of the invention of an alkylationreaction to produce ethylbenzene, wherein the dividing wall columndistillation is used to produce two side draw streams. A feed (302)comprising benzene and ethylene is fed to alkylation reactor (308). Thereactor (308) produces product stream (309) comprising benzene,ethylbenzene and polyethylbenzene.

The product stream (309) is then sent to a dividing wall distillationcolumn (312) that separates product stream (309) into an overhead stream(313), an upper side draw stream (322) comprising ethylbenzene product,a lower side draw recycle stream (316) comprising polyethylbenzene, anda bottoms residue stream (319). The overhead (313) is condensed incondenser (314), resulting in stream (315) that includes benzene andlighter components. Stream (315) may be recycled (not shown) back to thefeed stream (302). The lower side draw stream (316) comprisingpolyethylbenzene can be a recycle stream sent to a transalkylationreactor (330) to obtain recycle stream (332) that has a lowerpolyethylbenzene content than the lower side draw stream (316), that isthen mixed with the product stream (309) and sent to dividing walldistillation column (312). A portion of bottoms residue stream (319) issent back into the column via reboiler (320), while the remainingbottoms residue contains heavier components such as tetraethylbenzene iswithdraw in line (321).

FIG. 6 illustrates a dividing wall distillation column (412) thatseparates a mixed stream (402) into an overhead stream (413), an upperside draw stream (422), a lower side draw stream (416), and a bottomsstream (419). The mixed stream (402) is fed to the dividing walldistillation column (412) on the opposite side of the verticallypositioned dividing wall from the side draw streams (422) (416). Theoverhead (413) is condensed in condenser (414), resulting in stream(415), a portion of which will typically be used as a reflux stream forthe dividing wall distillation column (412). A portion of bottomsresidue stream (419) is sent back into the column via reboiler (420),while the remaining bottoms residue is withdraw in line (421).

Use of the term “optionally” with respect to any element of a claim isintended to mean that the subject element is required, or alternatively,is not required. Both alternatives are intended to be within the scopeof the claim. Use of broader terms such as comprises, includes, having,etc. should be understood to provide support for narrower terms such asconsisting of, consisting essentially of, comprised substantially of,etc.

As used herein, “parallel” or “parallel arrangement” is defined to meanthat the components are not arranged in series and that each componentseparately processes a portion of the stream. As such, the components donot have to be aligned in a true physical parallel manner with respectto each other.

Depending on the context, all references herein to the “invention” mayin some cases refer to certain specific embodiments only. In other casesit may refer to subject matter recited in one or more, but notnecessarily all, of the claims. While the foregoing is directed toembodiments, versions and examples of the present invention, which areincluded to enable a person of ordinary skill in the art to make and usethe inventions when the information in this patent is combined withavailable information and technology, the inventions are not limited toonly these particular embodiments, versions and examples. Other andfurther embodiments, versions and examples of the invention may bedevised without departing from the basic scope thereof and the scopethereof is determined by the claims that follow.

The invention claimed is:
 1. A method of ethylbenzene production comprising: obtaining a first product stream from an alkylation reaction zone; sending at least a portion of the first product stream to a dividing wall distillation column; removing an overhead stream and a bottoms stream from the dividing wall distillation column; and removing a side draw stream and a lower side draw stream from the dividing wall distillation column; wherein the first product stream is fed to the dividing wall distillation column at a location above where the side draw stream is taken; wherein the side draw stream comprises ethylbenzene.
 2. The method of claim 1, wherein the overhead stream comprises benzene.
 3. The method of claim 1, wherein at least a portion of the overhead stream is recycled to the alkylation reaction zone.
 4. The method of claim 1, wherein the lower side draw stream comprises polyethylbenzene.
 5. The method of claim 1, wherein at least a portion of the lower side draw stream is fed to a transalkylation reaction zone to produce a second product stream that has reduced polyethylbenzene content than the lower side draw stream.
 6. The method of claim 5, wherein at least a portion of the second product stream is fed to the dividing wall distillation column.
 7. The method of claim 1, wherein the dividing wall distillation column comprises between 20 and 100 equilibrium stages.
 8. The method of claim 1, wherein the dividing wall distillation column comprises between 40 and 80 equilibrium stages.
 9. The method of claim 1, wherein the dividing wall distillation column comprises packing.
 10. The method of claim 1, wherein the dividing wall distillation column comprises sieve trays.
 11. A method for the separation of hydrocarbon compounds comprising: obtaining a first stream comprising hydrocarbon compounds, wherein the first stream comprises a mixture of two or more aromatic compounds wherein one of the two or more aromatic compounds is ethylbenzene; sending at least a portion of the first stream to a dividing wall distillation column comprising a dividing wall; removing an overhead stream and a bottoms stream from the dividing wall distillation column; and removing a side draw stream from the dividing wall distillation column, wherein the side draw stream comprises ethylbenzene; wherein the first stream enters the dividing wall distillation column on an opposing side as the side draw stream, separated by the dividing wall; wherein the first stream is fed to the dividing wall distillation column at a location above where the side draw stream is taken; wherein the overhead stream comprises benzene and the bottoms stream comprises xylene.
 12. The method of claim 11, wherein the dividing wall distillation column comprises between 20 and 100 equilibrium stages.
 13. The method of claim 11, wherein the dividing wall distillation column comprises between 40 and 80 equilibrium stages.
 14. The method of claim 11, wherein the first stream is produced from a first reaction zone.
 15. The method of claim 14, wherein at least a portion of the overhead stream is recycled as feed to the first reaction zone.
 16. The method of claim 14, wherein at least a portion of the side draw stream is recycled as feed to the first reaction zone.
 17. The method of claim 14, wherein at least a portion of the bottoms stream is recycled as feed to the first reaction zone.
 18. The method of claim 11, wherein the dividing wall distillation column comprises packing.
 19. The method of claim 11, wherein the dividing wall distillation column comprises sieve trays. 